Deprecation and documentation for the AESCounterBuiltinRNG issue

* reproducer test of AESCounterBuiltinRNG issue
* update documentation of random-number-generator
* deprecate AES128CounterSecureRNG AES256CounterSecureRNG
* incorporate feedback from Johannes

akka-remote/src/main/scala/akka/remote/security/provider/DeprecatedAESCounterBuiltinRNG.scala

@@ -0,0 +1,147 @@
+/**
+ * Copyright (C) 2016-2018 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.remote.security.provider
+
+import java.security.{ Key, SecureRandom }
+import java.util.Random
+import java.util.concurrent.ThreadFactory
+import javax.crypto.Cipher
+import javax.crypto.spec.IvParameterSpec
+
+import akka.annotation.InternalApi
+
+import scala.concurrent.duration.{ Duration, FiniteDuration }
+import scala.concurrent.{ Await, ExecutionContext, Future, duration }
+
+/**
+ * INTERNAL API
+ *
+ * We cannot prove that this code is correct and it will therefore be removed
+ * with AES128CounterSecureRNG and AES256CounterSecureRNG. See security
+ * vulnerability https://doc.akka.io/docs/akka/current/security/2018-08-29-aes-rng.html
+ *
+ * This class is a Scala implementation of AESCounterRNG algorithm
+ * patterned after org.uncommons.maths.random by Daniel Dyer (Apache License 2.0)
+ *
+ * Non-linear random number generator based on the AES block cipher in counter mode.
+ * Uses the seed as a key to encrypt a 128-bit counter using AES(Rijndael).
+ *
+ * Keys larger than 128-bit for the AES cipher require
+ * the inconvenience of installing the unlimited strength cryptography policy
+ * files for the Java platform.  Larger keys may be used (192 or 256 bits) but if the
+ * cryptography policy files are not installed, a
+ * java.security.GeneralSecurityException will be thrown.
+ *
+ * NOTE: this class is not serializable
+ */
+@InternalApi
+private[akka] class DeprecatedAESCounterBuiltinRNG(val seed: Array[Byte], implicit val executionContext: ExecutionContext,
+                                                   val reseedingThreshold: Long     = CounterRNGConstants.ReseedingThreshold,
+                                                   val reseedingDeadline:  Long     = CounterRNGConstants.ReseedingDeadline,
+                                                   val reseedingTimeout:   Duration = CounterRNGConstants.ReseedingTimeout) extends Random {
+  import CounterRNGConstants._
+
+  private val entropySource = new SecureRandom
+
+  // mutable state below, concurrent accesses need synchronized or lock
+  private var index: Int = 0
+  private var currentBlock: Array[Byte] = null
+  private var reseedFuture: Future[Array[Byte]] = null
+  private var bitsSinceSeeding: Long = 0
+
+  private val cipher = Cipher.getInstance("AES/CTR/NoPadding")
+
+  // this algorithm can be further improved by better selection of the iv
+  // here and at re-seeding time further below
+  private val ivArr = Array.fill[Byte](CounterSizeBytes)(0)
+  ivArr(0) = (ivArr(0) + 1).toByte
+  private val ivSpec = new IvParameterSpec(ivArr)
+  cipher.init(Cipher.ENCRYPT_MODE, new this.AESKey(seed), ivSpec)
+
+  private val zeros: Array[Byte] = Array.fill[Byte](CounterSizeBytes)(0)
+
+  @Override
+  override protected def next(bits: Int): Int = synchronized {
+    // random result generation phase - if there is not enough bits in the currentBlock
+    // we generate some more with AES/CTR
+    bitsSinceSeeding += bits
+    if (currentBlock == null || currentBlock.length - index < 4) {
+      try {
+        currentBlock = cipher.update(zeros)
+        index = 0
+      } catch {
+        case ex: Exception ⇒
+          // Generally Cipher.update() from nextBlock may throw various exceptions.
+          // However this should never happen.  If initialisation succeeds without exceptions
+          // we should be able to proceed indefinitely without exceptions.
+          throw new IllegalStateException("Failed creating next random block.", ex)
+      }
+    }
+
+    // now, enough bits in currentBlock, generate pseudo-random result
+    val result = (BitwiseByteToInt & currentBlock(index + 3)) |
+      ((BitwiseByteToInt & currentBlock(index + 2)) << 8) |
+      ((BitwiseByteToInt & currentBlock(index + 1)) << 16) |
+      ((BitwiseByteToInt & currentBlock(index)) << 24)
+
+    // re-seeding phase
+    // first, we check if reseedingThreshold is exceeded to see if new entropy is required
+    // we can still proceed without it, but we should ask for it
+    if (bitsSinceSeeding > reseedingThreshold) {
+      if (reseedFuture == null) {
+        // ask for a seed and process async on a separate thread using AESCounterBuiltinRNGReSeeder threadpool
+        reseedFuture = Future { entropySource.generateSeed(seed.length) }
+      }
+      // check if reseedingDeadline is exceeded - in that case we cannot proceed, as that would be insecure
+      // we need to block on the future to wait for entropy
+      if (bitsSinceSeeding > reseedingDeadline) {
+        try {
+          Await.ready(reseedFuture, reseedingTimeout)
+        } catch {
+          case ex: Exception ⇒
+            Console.err.println(s"[ERROR] AESCounterBuiltinRNG re-seeding failed or timed out after ${reseedingTimeout.toSeconds.toString}s !")
+        }
+      }
+      // check if future has completed and retrieve additional entropy if that is the case
+      if (reseedFuture != null && reseedFuture.isCompleted) {
+        if (reseedFuture.value.get.isSuccess) { // we have re-seeded with success
+          val newSeed = reseedFuture.value.get.get // this is safe
+          cipher.init(Cipher.ENCRYPT_MODE, new this.AESKey(newSeed), ivSpec)
+          currentBlock = null
+          bitsSinceSeeding = 0 // reset re-seeding counter
+        }
+        reseedFuture = null // request creation of new seed when needed
+      }
+    }
+
+    index += 4
+    result >>> (32 - bits)
+  }
+
+  /**
+   * Trivial key implementation for use with AES cipher.
+   */
+  final private class AESKey(val keyData: Array[Byte]) extends Key {
+    def getAlgorithm: String = "AES"
+    def getFormat: String = "RAW"
+    def getEncoded: Array[Byte] = keyData
+  }
+}
+
+private object CounterRNGConstants {
+  final val CounterSizeBytes = 16
+  final val BitwiseByteToInt = 0x000000FF
+  final val ReseedingThreshold = 1000000000L // threshold for requesting new entropy (should give us ample time to re-seed)
+  final val ReseedingDeadline = 140737488355328L // deadline for obtaining new entropy 2^47 safe as per SP800-90
+  final val ReseedingTimeout: FiniteDuration = Duration.apply(5, duration.MINUTES) // timeout for re-seeding (on Linux read from /dev/random)
+}
+
+private class AESCounterBuiltinRNGReSeeder extends ThreadFactory {
+  override def newThread(r: Runnable): Thread = {
+    val thread = new Thread(r, "AESCounterBuiltinRNGReSeeder")
+    thread.setDaemon(true)
+    thread
+  }
+}